The present invention relates to minesweeping equipment, and more particularly to equipment that will clear a body of water of mines that can be set off by influence signatures.
A minesweeping system that creates influence signatures generally must provide a large enough influence field to be effective while still minimizing the size and weight of the equipment to make the system practical from the standpoint of the platform which controls and/or tows the system. This platform may be a ship, a helicopter, a remote controlled vehicle operating above or below the water surface, or a slow moving aircraft. Minesweeping systems generally have therefore involved a trade-off of performance vis-a-vis size and weight.
Prior art systems to date have included sweep systems using open loop magnetic technology, wherein electrical current is distributed between two or more towed electrodes and the intervening seawater between the multiple electrodes is used as the electrical return. One such system, the Mk-105, utilizes a hydrofoil vehicle towed by a helicopter with a gas turbine power plant on the hydrofoil to generate electricity for the open loop electrodes. The Mk-105 system is powerful, but also quite large and heavy, thus requiring the hydrofoil vehicle. In general, however, the most efficient means to achieve a large magnetic field is to use the open loop means of generating the field. Thus, a ship or helicopter-hydrofoil system has generally been required for the towing. Further, such open loop systems require sufficient physical handling equipment to handle the two or more electrodes, including the appropriate deployment and retrieval of the multiple electrodes as well as maintaining the multiple electrodes separated from one another for proper functioning and to avoid tangle.
An alternative prior art sweep system, for example the SWIMS system, generates the magnetic influence field utilizing conventional dipole technology with large magnetic cores. Because of the size and weight associated with this technology, however, the magnetic field is limited by the size and weight of a practical towed body in which the system is housed.
Still further prior art minesweeping systems have involved various coils or permanent magnet solutions which also have size and weight problems that result in limited field strength.
My pending U.S. patent application Ser. No. 09/545,820 filed Apr. 7, 2000, discloses an open loop minesweeping system, but one which is smaller than the above-referenced prior art, lightweight, and having simplified electrode handling. A body is towed in the water by a tow cable, the body towing only one (the first) electrode behind it while still using the open loop means of generating the magnetic field. This is accomplished by having the towed body itself function as the other (second) electrode, either by making the skin of the towed body the electrode or by having removable panels on the skin of the towed body. AC input power of low amperage and high voltage is passed from the primary towing platform to the towed body, the AC power then being transformed and rectified at the towed body.
The present minesweeping invention also is intended to utilize the open loop means of generating the magnetic field to obtain a powerful field, while overcoming the deficiencies of the prior art to provide a smaller system, a lightweight system, and a system that simplifies electrode handling. The present invention is sufficiently small and stable that it can be utilized with and towed by smaller helicopters, smaller water vehicles or remotely operated vehicles. The invention is adapted to a wide variety of littoral or deep water operations, for example to clear mined ports or offshore areas or off a beachhead or deep water areas such as choke points.
The present invention includes a body to be towed in the water by a tow cable, the body containing hydrodynamic control surfaces and designed to provide a high-speed and stable tow. The body provides the means to generate the magnetic influence signatures, and the body may also include transducers to generate acoustic influence signatures. A significant aspect of the present invention, as in my above-referenced pending patent application, is that the towed body also does not tow multiple electrodes behind it to generate magnetic signatures, but rather only tows one (the first) electrode behind it while still using an open loop means of generating the magnetic field. This is accomplished in the present invention by having the other (second) electrode positioned along the tow cable itself ahead of the towed body. In particular, a plurality of spaced fairings may be attached to the tow cable. Each fairing has a first conductive portion electrically isolated from the conventional electromechanical tow cable, and a second non-conductive portion mechanically attached to the tow cable. The conductive portions of the fairings are electrically connected together to form the second electrode which is electrically fed from the towed body. Since the towed body only tows one cable which contains the first electrode extending behind the towed body, the physical handling equipment for the single cable is thus considerably simplified as contrasted with what is needed for open loop systems handling and towing multiple cables, each with electrodes. As an alternative to the fairing approach, the other (second) electrode may be an electrode cable positioned along and tied to the tow cable.
Open loop power and control systems generally provide an input AC power which is then rectified to DC power and controlled to either continuous level or to relatively low frequency (pulsed) waveforms. This rectification and conditioning generally are done on the primary towing platform, i.e., the helicopter or ship, which requires weight and space, and requires large diameter cables to handle and pass the large DC currents associated with open loop sweeps. Particularly when the primary towing vehicle is a helicopter, the cable with DC power from the helicopter to the towed body is in air and thus presents difficulties in cooling absent such a large diameter cable. Accordingly, in a further aspect of the present invention, as in my above-referenced pending patent application, AC input power of low amperage and high voltage is passed from the primary towing platform to the towed body, enabling the use of a lower weight cable of small diameter that can be handled by a small helicopter. The AC power is then transformed and rectified at the towed body.
Although the transformer and rectifier components would normally generate excessive and damaging heat at the towed body, the heat is dissipated in the present invention, as in my above-referenced pending patent application, by exposing the transformer and rectifier components at the towed body directly to the sea water. These components are not retained within a watertight enclosure with cooling mechanisms, but are encapsulated within a thin waterproof coating directly exposed to the sea water, the coating protecting the components from the conductive sea water but otherwise cooling the components by passing heat through the thin coating directly to the sea water. Maximum cooling is obtained, and the components can be of significantly reduced size and weight from that which would be required by alternative forms of cooling at the towed body.
The body to be towed also may contain a winch to deploy and return the first electrode. The first electrode also may take alternative forms, such as a cable, a rigid sleeve, or a flexible sock as disclosed in my above-referenced pending patent application.